Networks of cellular systems are typically divided into a Radio Access Network RAN and a Core Network CN. Presently the third generation (3G) radio systems are being standardized. One 3G system will be based on WCDMA technology, Wide-band Code Division Multiple Access, over the air interface and thus this technology will be used in the RAN, whereas the CN will be similar to the one existing in GSM (Global System for Mobile communications).
FIG. 1 presents a block diagram of the system architecture of a 3G system. The system comprises the elements shown in FIG. 1, i.e. a mobile station MS, the RAN (marked UTRAN, UMTS Terrestrial RAN where UMTS stands for Universal Mobile Telecommunications System), and the CN. The mobile station MS is radio connected to at least one base station BTS which is connected to a radio network controller (RNC) over the so called lub interface (and two RNCs may be connected with each other over the so called lur interface). Further the RAN is connected to the CN over the lu interface. As shown in the figure the RNC is connected to the MSC (Mobile services Switching Centre) including the VLR (Visitor Location Register) and to the SGSN (Service GPRS Support Node, where GPRS is General Packet Radio Service that is standardized in GSM). Further the SGSN is connected to the GGSN (Gateway GPRS Support Node) and the MSC is connected to the GMSC (Gateway MSC). As seen in the figure at least the MSC, GMSC and SGSN have a connection to the HLR (Home Location Register) and SCP (Service Control Point). The connection to other networks go via the GMSC and the GGSN, where typically circuit switched communication would go via the MSCs (i.e. via the MSC and GMSC) and packet switched communication would go via the GSNs (i.e. via the SGSN and GGSN).
The radio frequencies that the 3G system (that will be based on WCDMA, Wide-band Code Division Multiple Access) will use (in communication between the MS and the BTS) have been agreed by different standardization bodies, and in several countries licenses to build 3G networks have been sold to operators on auctions. These licenses have been tremendously expensive. Also building up a new network additionally requires huge investments to be made on equipment and there therefore exists questions how the operators will be able to make profit and pay off the investments with the 3G system. Moreover, in certain countries there has been given a requirement of a certain (minimum) coverage area in order for the operator to get the 3G network license.
Therefore there is a clear need to seek solutions for saving costs in relation to these new networks.
Document WO 01/15471 discloses the use of two parallel core networks for one BSS (base station sub-system) in order to increase the core network capacity of an operator's network by dynamically spreading the load between the two core networks. When the mobile terminal registers its presence in the location area, the BSS will forward the request dynamically to either of the two core networks based on the core network loading. The solution shown does not save costs but rather adds costs if an operator would use two core networks for each BSS. Further a drawback of the solution described in the WO document is that it can not be implemented as such according to the existing mobile network standards, but would require a change of the present standards.